Random copolymerization



United States Patent Public Int. Cl. C08d ]/32 US. Cl. 260-843 6 Claims ABSTRACT OF THE DISCLOSURE A random copolymer of a conjugated diene and a vinylsubstituted aromatic compound is formed using an organolithium initiator, an organo-alkali metal compound such as potassium tert-butoxide, and a hexaalkylphosphoramide such as hexamethylphosphoramide.

This invention relates to a method for forming random copolymers. In one aspect this invention relates to a randomizing composition for forming random copolymers.

Heretofore organolithium compounds have been used to copolymerize monomers such as butadiene and styrene in a hydrocarbon diluent and block copolymers were formed. In order to obtain a random copolymer an additional compound was added. This additional compound is hereinafter called a randomizing agent or randomizer. Polar compounds such as ethers were used as a randomizer but a high vinyl content coploymer was formed. In general, with the use of certain organo-alkali metal randomizing agents, it was found that a low vinyl content random copolymer was former but substantial amounts of homopolymer blocks were also formed when the ratio of the atoms of alkali metal in the randomizing agent to the atoms of lithium in the initiator was less than 0.05:1. Also, hexaalkylphosphoramides have been used as randomizing agents but it was generally found that, although a low vinyl content random copolymer was formed, when the ratio of the mols of hexaalkylphosphoramide to the equivalents of lithium in the initiator was less than 0.2:1 substantial amounts of homopolymer blocks were formed in the copolymer product.

Quite surprisingly, it has now been found in the copolymerization of at least two members selected from the group consisting of conjugated dienes and vinyl substituted aromatics with an organolithium initiator in the presence of an organo-alkali metal randomizer in an atom ratio range of alkali metal in the randomizer to lithium in the initiator of from 0.05:1 to 0.007:l substantially completely random low vinyl copolymers are formed, i.e. substantially no homopolymer blocks are present in the copolymer product, when a hexaalkylphosphoramide is also used in a ratio of mols of phosphoramide to atoms of lithium in the initiator in the range of from 0.211 to 0.01:1, preferably 0.1:1 to 0.01:1.

Also according to this invention, a randomizing composition is provided for organolithium initiated copolymerization in the form of a combination of an organoalkali metal compound and a hexaalkylphosphoramide, said organo-alkali metal compound and said hexaalkylphosphoramide being present in amounts sufiicient to provide the ratios for those compounds relative to the organolithium initiator as set forth in the preceding paragraph, i.e. the ratio of alkali metal atoms in said organoalkali metal compound to mols of hexaalkylphosphoramide is from about :1 to about 0.035z1, preferably from about 5:1 to about 0.07:1.

Accordingly, it is an object of this invention to provide a new and improved method for forming random copolymers. Another object of this invention is to provide a new and improved randomizing composition.

Other aspects, objects and the several advantages of this invention will be readily apparent to those skilled in the art from the description and the appended claims.

The. term random copolymer as applied to the polymer product of this invention is intended to include products ranging from those in which there is substantially no detectable homopolymer block, e.g. polyvinyl aromatic block up to copolymers containing about 1 weight percent of a homopolymer block. In general, the monomers, catalyst, and hydrocarbon diluent as well as the process conditions disclosed in US. Patent 2,975,160, issued to R. P. Zelinski on Mar. 14, 1961, the full dis closure of which is hereby incorporated herein by reference, can be employed in preparing the random co polymers of this invention.

The conjugated dienes that can be employed contain from 4 to 12 carbon atoms per molecule but preferably are 1,3-butadiene, isoprene, and piperylene. Mixtures of conjugated dienes can be used as well as mixtures of vinyl substituted aromatics and mixtures of conjugated dienes with vinyl substituted aromatic compounds. It is presently preferred that the monomer mixture contain at least one conjugated diene and at least one vinyl substituted aromatic. Examples of vinyl substituted aromatic compounds include styrene, divinylbenzene, vinylnapthalenes such as l-vinylnapthalene, and alkyl substituted vinyl aromatics in Which the alkyl group is attached to the. ring, such as 3 methylstyrene, and the like.

Any member of the known class of organolithium polymerization initiators can be used. These initiators are organic compounds which have at least one carbonlithium bond and generally are otherwise hydrocarbon but can contain functional groups which are inert to the polymerization reaction. The lithium compound most commonly used is that having the formula RLi where R is an aliphatic, cycloaliphatic or aromatic hydrocarbon radical having about 1 to 20 carbon atoms and x is an integer from 1 to 4. Examples of such compounds include methyllithium, n-butyllithium, phenyllithium, cyclohexyllithium, 1,S-dilithio-naphthalene, and the like. The amount of initiator used is generally in the range of from about 0.05 to about 150 millimoles, preferaly 0.5 to 20 millimoles per parts by weight of monomer.

The polymerization is preferably carried out in the presence of a hydrocarbon diluent which can be one or more aromatic, parafiinic, or cycloparafiinic compounds, preferably containing 4-10 carbon atoms per molecule. The solvent is a liquid under the conditions of the process, suitable examples being butane, n-pentane, isooctane, cyclohexane, benzene, toluene, xylene, ethylbenzene, hexane, and the like. Mixture of these solvents can be used.

The polymerization temperature can vary over a broad range, for example from -20 to 150 C., although a temperature less than 20 C. is seldom employed and a preferred temperature range is about 30 to C. Pressure used is sufficient to maintain a substantially liquid phase in the reaction Zone.

Upon completion of the polymerization reaction a shortstop such as Water, and alcohol, e.g. ethyl alcohol or isopropyl alcohol and organic or inorganic acid, or other catalyst inactivating agent is employed and the polymer product recovered by any conventional method depending upon the type of polymer, i.e. rubbery, liquid and the like, formed. After inactivation of the catalyst and addition of any conventional additive such as antioxidant the polymer can be recovered by a technique such as coagulation with an alcohol such as ethyl alcohol or isopropyl alcohol, stripping of the diluent or the like. One method which can be employed comprises exposing the polymerization mixture to a reduced pressure to cause flashing of the diluent. The conditions in the flashing zone are controlled so as to remove up to about 50 percent of the diluent. Any unreacted monomer can also vaporize along with the diluent. Steam stripping can also be employed for forming a slurry of polymer crumb which crumb is then recovered and dried in a conventional manner.

The organo-alkali metal compound of the randomizing composition of this invention can be one or a mixture of two or more of compounds having the following formulas:

matic radicals, preferably containing from 1 to 6 carbon atoms, Q is selected from the group consisting of radicals, wherein R" is as defined above, at is an integer from 4 to 5, inclusive, and y is an integer from 1 to 3, inclusive, R is selected from the group consisting of aliphatic, cycloaliphatic and aromatic radicals, preferably containing from 4 to carbon atoms, Y is selected from the group consisting of oxygen and sulfur and n is an integer from 1 to 3, inclusive. It is to be understood that the aliphatic and cycloaliphatic radicals mentioned above can be saturated or unsaturated. Presently preferred organo-alkali metal compounds are the alkali metal salts, especially sodium and potassium salts, of a monohydric alcohol having from 1 to 20, more preferably 1 to 10, carbon atoms per molecule, inclusive.

Examples of organometal compounds corresponding to Formula 1 include the following: methylsodium, ethylpotassium, n-propylrubidium, isopropylcesium, tert-butylsodium, tert-amylsodium, n-hexylpotassium, cyclohexylrubidium, eicosylcesium, 4-methylcyclohexylsodium, 3- hexenylsodium, 2,5-decadienylpotassium, 3-cyclopentenylrubidium, 4,6-di-n-butyldecylsodiu-m, 3,6-djphenyloctylpotassium, phenylsodium, l-naphthylpotassium, 4-tolylpotassium, benzylsodium, 4-tert-butyl-6,7-diisopropyl-2- naphthylpotassium, and the like.

Formulas 2 and 3 define the alkali metal salts of monoand polyhydric alcohols, monoand polyhydric phenols, including bis-phenols, and sulfur analogs of the foregoing, that can be used in preparing the present catalyst system. Specific examples of compounds represented by Formula 2 include the sodium, potassium, rubidium, and cesium salts of methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, tert-butyl alcohol, tert-amyl alcohol, n-hexyl alcohol, cyclohexyl alcohol, eicosyl alcohol, 2- butenyl alcohol, 4-methylcyclohexyl alcohol, B-hexenyl alcohol, 2,5-decadienyl alcohol, 3-cyclopentenyl alcohol, 4,6-di-n-butyldecyl alcohol, 4,8-dodecadienyl alcohol, allyl alcohol, l,3-dihydroxyhexane, 1,5,9-trihydroxytridecane, 1,6-dihydroxyoctane, 1,9,l5-trihydroxypentadec ane, benzyl alcohol, 3(4-tolyl)propyl alcohol, phenol, catechol, resorcinol, hydroquinone, pyrogallol, l-naphthol, Z-naphthol, 2,6-di-tert-butyl-4-methylphenol (Ionol), 2,4,6-tri-tert-butylphenol, 2,6-di-tert-butylphenol, 2,6-ditert-butyl-4-phenylphenol, 2,6-di-sec-butyl 4 methylphenol, ethanethiol, l-butanethiol, 2-pentanethiol, 2-isobutanethiol, benzenethiol (thiophenol), l,l2-dodecanedi thiol, 5,9-di-n-propyl-1,14-tetradecanedithiol, 2-naphthalenethiol, cyclohexanethiol, 2,5-di-n-hexyl-6-terbbutylbenzenethiol, 2,6-di-tert-butyl-4(4-tolyl)benzenethiol, 3- methylcyclohexanethiol, Z-naphthalenethiol, benzenemethanethiol, Z-naphthalenemethanethiol, 1,8-octanedithiol, 1,10-decanedithiol, l,4-benzenedithiol, and the like. Specific examples of suitable compounds corresponding to Formula 3 are the sodium, potassium, rubidium and cesium salts of 2,2'methylene-bis(4-methyl-6-tert-bntylphenol), 2,2-isopropylidene-bis(4-cyclohexyl p cresol), 4,4-isopropylidenebis( 2,6-dicyclohexylphenol) 4,4-methylene-bis(2,6-diisopropylphenol), 2,2 methylene bis(6 benzyl-p-cresol), 2,2'-ethylidene-bis(5 isopropylphenol), 1 l-bis (4-hydroxyphenyl) cyclohexane, 1,1 -bis Z-hydroxy- 3-(3-tolyl) ]cyclopentane, 2,2 ethylidene bis(4-ethyl-6 tert-hexylthiophenol) 2,2-propylidene-bis- 3,5-dimethyl- 6-cyclopentylthiophenol) 4,4 thio-bis(2,6 di-tert-butylphenol), 4,4'-dithio-bis(Z-n-propyl 6 tert-butylphenol), 4,4-trithio-bis(3-methyl-fi-isopropylphenol), and the like.

Specific examples of the alkali metal salts of monoand polycarboxy acids and sulfur analogs as represented by Formula 4 include the sodium, potassium, rubidium and cesium salts of isovaleric acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, oleic acid, ricinoleic acid, linoleic acid, linolenic acid, gadoleic acid, cyclopentanecarboxylic acid, dimethylcyclohexane-3,5-dicarboxylic acid, phenylacetic acid, benzoic acid, pimelic acid, azelaic acid, sebacic acid, phthalic acid, hendecane-l,l1-dioic acid, 1,8,16-hexadecanetricarboxylic acid, 3,3,7,7-tetramethylnonane-1,5,9-tricarboxy1ic acid, 4-pentyl-2,5-heptadiene-1,7-dioic acid, 2-naphthoic acid, l-naphthaleneacrylic acid, hexanethionic acid, 2,2- diethylbutanethiolic acid, decanethionic acid, tridecanethionothiolic acid, 4-tetradecanethionic acid, thiolbenzoic acid, thiono-l-naphthoic acid, and the like.

Specific examples of alkali metal carbonates and sulfur analogs as represented by the Formula 5 include the sodium, potassium, rubidium and cesium salts of tertbutylcarbonic acid, n-hexylcarbonic acid, 3,5-dimethylhexylcarbonic acid, n-dodecylcarbonic acid, 4,4-diethylhexylcarbonic acid, 3,6-diphenyloctylcarbonic acid, 7- dodecenylcarbonic acid, 3-cyclohexenylcarbonic acid, phenylcarbonic acid, O-tcrt-amyl ester of thiolcarbonic acid, O-tridecyl ester of thionocarbonic acid, O-eicosyl ester of thionothiocarbonic acid (xanthic acid), S-hexadecyl ester of dithiolcarbonic acid, S-(3-cyclohexenyl) ester of thiolcarbonic acid, phenyl ester of trithiocarbonic acid, and the like.

Specific examples of alkali metal salts of secondary amines as represented by Formula 6 include the sodium, potassium, rubidium and cesium salts of dimethylamine, di-n-butylamine, methyl-n-hexylamine, di(3,5-diethyloctyl) amine, di( 8-phenyloctyl amine, di S-hexenyl) amine, diphenylamine, dibenzylamine, ethyl-4-tolylamine, n-propyl-n-eicosylamine, and the like.

The component which is added to the butylithiumorgano-alkali metal system and thereby allows the production of substantially completely random copolymers notwithstanding the relatively small amount of randomizing agents employed relative to the organolithium int tiator 1s a hexaalkylphosphoramide and is represented by the formula tyllithium, and then the potassium tert-butoxide. Conversion was quantitative in all runs. At the end of the polymerization, each reaction was terminated with a solution of 2,2-methylene-bis(4-methyl-6-tert-butylphenol) in a f mixture of equal parts by volume of toluene and isopro- O=PN pyl alcohol, the amount used being sufiicient to provide approximately one part by weight of the antioxidant per 100 parts by weight of polymer. The product was coagulated in isopropyl alcohol, separated, and dried. Results R are presented in Table I.

TABLE Mierostructure, Etiective Efiective percent,normalired HMPA, t-BuOK, Effective t-BuOK/BuLi, HMPA/BuLi, Polystyrene? mhm. mhm BuLi,mhm. mole ratio mole ratio Cis Trans Vinyl percent 0.01 0. 01 0.6 0. 0167 0. 0167 39.2 52.0 8.8 0,5 0. 01 0.02 0.6 0.0333 0. 0167 37.7 52.0 10.3 0 0. 01 0. 03 0.6 0. 05 0.0167 38.4 49.7 11.9 0 0. 02 0. 01 0.6 0. 0167 0.0333 39.2 51.5 9.3 0.1 0.02 0.02 0.6 0.0333 0.0333 38.1 51.6 10.3 0 0. 02 0.03 0.6 0. 05 0. 0333 38.6 49.7 11.7 0 0. 03 0. 01 0.6 0.0167 0.05 37.7 52.3 9.5 0.6 0. 03 0. 02 0.6 0.0333 0. 05 35.6 53.6 10.3 9 0. 03 0. 03 0.6 0. 05 0. 05 35.3 52.3 12.4 0 0.04 0. 01 0.6 0. 0167 0. 067 37.3 52.7 10.0 0 0.04 0. 02 0.6 0.0333 0.067 37.5 51.6 10.9 0 0. 04 0. 03 0.6 0.05 0.067 36.9 50.7 12.4 0 1 Determined by infrared analysis. 2 Determined by oxidative degradation.

where each R is the same or a different alkyl radical con- These data Show that With extremely small amounts taining from 1 to 8 carbon atoms. The compounds have of the two randomizers of this invention a substantialhigh boiling points and are soluble in the hydrocarbon 1y completely random copolymer is obtained. diluent used for the polymerization. For example, hex- Reasonable variations and modifications are possible amethylphosphorarnide has a boiling point of 76 C. at within the scope of this discolsure without departing from a pressure of 1 mm. Hg. Other compounds of this type the spirit and scope thereof. include hexaethylphosphoramide, heXa-n-propylphosphor- I claim: amide, and hexaoctylphosphoramide, hexaisopropylphos- 1. The polymerization process for copolymerizing phorarnide, trimethyltrihexylphosphoramide, dipropyltetmonomers including at least one conjugated diene and at t l h h id d th like, least one vinyl-substituted aromatic compounds compris- As stated before, by this invention amounts of organoing contacting said monomers under copolymerization alkali metal randomizers are employed which heretofore conditions in the presence of a solvent selected from yielded a polymer product containing substantial amounts, aromatic, paraffinic, cycloparaffinic compounds, and mixe.g. 20 percent, of homopolymer blocks and that by the tures thereof, with a randomizing catalyst composition addition of amounts of hexaalkylphosphoramide also hereconsisting essentially of an organolithium initiator, an tofore thought to produce a product polymer containing organoalkali metal compound of the formula: R'(OM),,, substantial amounts of homopolymer blocks, a substanwherein R is an aliphatic radical having from 1 to 20 tially completely random copolymer is obtained. Thus, by carbon atoms, M is an alkali metal selected from sodium, the combination of the organo-alkali metal and hexaalkylpotassium, rubidium, and cesium, O is oxygen, and n is phosphorarnide randomizers, a surprisingly lower amount an integer from 1 to 3, inclusive, and hexaphosphorof randomizers than heretofore thought necessary pro amide of the formula duces a substantially completely random copolymer. R R

EXAMPLE R VI A series of runs was made for the copolymerization do 0:1 N of butadiene with styrene in the presence of n-butyllithium, potassium tert-butoxide, and hexamethylphosphoramide to produce random copolymers. Each of the randomizing agents was used in very small quantities. The R Polymenzauon Tempe was as follows: wherein R is an alkyl radical containing from 1 to 8 car- 1,3-butadiene, parts by weight 75 on atom said organoalkali metal compound being Styrene, parts by weight 25 P ese in n a nt 0 provide a ratio Of alkali atoms Cyolohexane, parts by weight 780 in said organoalkali metal compound to mols of hexan-Butyllithium (BuLi), mhm 2 1.0 ph ph ramide in the range of from 5:1 to about 0.035: 1, Hexamethylphosphoramide (HMPA), mhm Vari ble said hexaphosphoramide being present in a ratio of mols Potassium t rt-b id (t-B OK) h V bl of hexaphosphoramide to atoms of lithium in said initi- Temperature, F 122 ator of from 0.211 to 0.01:1 and wherein said organo- Time, hours 18 lithium initiator is in a concentration to provide .05 to l Gram millimoles per 100 grams monomers 150 millimoles per IOO prats by weight monomer. 2 Scavenger level, 0.4 mhm.; efiective butyllithium level, 2. The process of claim 1 wherein said monomers are 05 butadiene and styrene, said organolithium initiator is Cyclohexane was charged first after which the reactor butyllithium, said organoalkali metal compound in po- Was purged with nitrogen. Butadiene and styrene were tassium tert-butoxide and said hexaphosphoramide is added followed by the hexamethylphosphoramide, the buhexamethylphosphoramide.

wherein R is an alkyl radical containing from 1 to 8 carbon atoms, said organoalkali metal compound being present in a ratio of alkali atoms in said organoalkli metal compound to mols of phosphoramide in the range of form about 5:1 to about 0.035: 1, said phosphoramide being present in a ratio of mols of phosphoramide to atoms of lithium in said initiator of from 0.211 to 0.01:1 and wherein said randomizing catalytic composition is in the presence of a solvent selected from aromatic, paraffinic, cycloparaffinic compounds, and mixtures thereof.

4. A composition according to claim 3 wherein said organolithium initiator is selected from the group having the formula RLi where R is an aliphatic, cycloaliphatic or aromatic hydrocarbon radical having from 1 to 20 carbon atoms and x is an integer of from 1 to 4, said organo-alkali metal compound is potassium tert-butoxide, and said phosphoramide is hexamethylphosphoramide.

5. A composition according to claim 3 wherein said phosphoramide is present in a ratio of mols of phosphoramide to atoms of litium in said initiator of from 0.121 to 0.01:1.

6. A composition according to claim 3 wherein said organo-alkali metal is one of sodium and potassium, and n is 1.

References Cited UNITED STATES PATENTS 3,366,611 1/1968 Wofiord 260-84.7 3,288,872 11/1966 House 260--669 3,324,191 6/1967 Wofi'ord 260669 JOSEPH L. SCHOFER, Primary Examiner J. C. HAIGHT, Assistant Examiner US. Cl. X.R. 

